New Adaptive Hybrid-Automatic Irrigation Control System for Soilless Culture

Abstract

In soilless culture, irrigation scheduling is an important and difficult task, as water and nutrients must be frequently and precisely applied, due to the reduced volume and low water holding capacity of most of the substrates. This paper describes an efficient control system for irrigation management of soilless culture based on an irrigation tray and a new adaptive hybrid automatic irrigation control algorithm. The proposed irrigation scheduling criteria are based on applying constant amounts in every irrigation application and variable timing as a function of crop water consumption. The control system analyzes the water balance in the control tray from the information provided by the sensors on the measured inputs and outputs of water from the tray. A hybrid algorithm composed of two stages is proposed. An estimation of the irrigation interval between irrigations is made by using an average daily crop water uptake pattern obtained from the feedback information of the tray. Short-term variations of the crop water uptake from the average daily pattern are adjusted by applying a proportional-integral (PI) controller. A field test was conducted to assess the performance of the proposed control system. The irrigation controller performed reasonably well as it fitted the leaching fraction for most of the irrigation events to the target value and its productive results were comparable to the ones obtained in a radiation-based control treatment.